1. Field of the Invention
The invention is related to a system (process and device) in order to get a perfect winding structure during the winding of web-like products especially made of paper to produce at least one wound paper web roll on a winding machine, with a pair of drums for supporting and starting the rotation of at least one wound paper web roll which is positioned in a winding bed made by the supporting drums, at least one of which preferably comprises an elastic flexible surface such as for example, a rubber cover. There are cooperating means, comprising a tensioned incoming traveling paper web, torque differentiation between the supporting drums and a rider roll engaging web roll being wound, all controlled by a computer which coordinates the elements of web tension, torque on the support drums and nip load provided by the roll to change the tensile stress remaining in the wound part.
2. Description of the Prior Art
In the above mentioned winding machines known in the art, the former supporting drums did not have an elastic flexible surface. Then, the winding structure could be influenced in such a way that the distribution of weights on the supporting drums was different and variable during the winding process and the pressure provided by the rider roll was dependent on the diameter of the roll, and was variable as well. Typically, the load on the supporting drum roll that was not wrapped by the web was linearly decresed depending on the increasing diameter of the roll, whereas the load on the first supporting drum in the winding direction (i.e., the so-called back drum) was linearly increased. The initial and final load values were controllable. It was typical as well that the load exerted by the rider roll to the web roll at first was increased according to the diameter of the roll, then decreased and did not exist any more at a defined diamter of the roll. The load itself was changeable.
It was typical as well that the tension exerted on the web that had to be wound was constant-independent of the diameter of the roll. Thus, the roll qualities of conventional two-drum winders, the supporting drums of which had a basically unflexible surface, could be improved.
The winding parameters did in no way take into account the friction values between the web and the supporting drums. Thereby, the forces exerted on the supporting drums and to the rider roll sometimes could not be transferred to the web. As a consequence slippage occured with respect to the web and the winding structure of the roll became insufficient.
The two-drum winders with at least one supporting drum with an elastic flexible surface (softnip principle) that were introduced in the market in the meantime were not successful with respect to the means for changing the wound tension of the web.
DE-GM 87 08 849 discloses a winder with two parallel drums and a rider roll that can be tilted as a whole to control the nip pressure. At the beginning of the winding process the rider roll exerts high pressure on the winding roll starting to build up. A tight core is obtained by this pressure, and also a positive speed differential between the drums and a corresponding back tension. During the following winding process the pressure of the rider roll is reduced. The back tension and the tilting of the whole winder is used to control the quality of the wound paper web rolls, i.e. the hardness. It is possible to provide the drums, especially the front drum with different coatings, i.e. a rubber coating.
A method for controlling the hardness of a winding roll by application of a different torque on back and front drum is disclosed in DE-A1-29 32 396. Hardness and the difference of the driving electrical current to apply different torque at the two drums follow according to the diameter of the roll. Hardness and current difference are kept at a constant value during a first phase. Afterwards, these values are decreased linearly. During a third phase these values are kept at a constant lower level. The first phase may be omitted. Neither a change of the back tension of the web nor a rider roll is revealed in this document.
GB-A-21 17 395 discloses a two drum winder with a rider roll whereby the web tension is controlled by controlling the speed difference between the two drums in dependence on the diameter of the roll which is already wound and in response to given speed signals representative of the speed of rotation of each drum. The torque of each drum follows a curve as depending on the speed differential and on the diameter of the winding roll. The torque curves can be divided into three phases. The torque on both drums is constant during the first and the third winding phase. While in the middle (i.e., intermediate portion) of the winding phase, the torque on the front drum is decreasing and the torque on the back drum is increasing at the same time. According to this document it is desired to keep the web tension constant throughout the roll. A method how to control the pressure exerted by the rider roll is not disclosed.
While GB-A-21 17 935 proposes to keep the wound-in tension of the web contact throughout the wound roll, the document FR-A-24 36 633 also teaches that the web tension should be kept constant during the first phase of winding, but on an elevated level, while roll diameter increases, and that the web tension should decrease after a first roll diameter D1 is reached and should be kept constant after a nominal tension at a second diameter D2 is reached, whereafter web tension will decrease again for the rest of the winding operation after a third diameter D3 is reached. However, no technical means is disclosed in the document as to how to achieve a web tension variation as hereinabove explained.
The invention starts from the general teaching of the FR-A-24 36 633 document, i.e., that during winding operation the wound-in tension of the web should be at an elevated level at the beginning of the winding operation and be decreased below the nominal tension towards the end of the winding operation.
While GB-A-21 17 935 and FR-A-24 36 633 documents propose to change the wound-in tension of the web formed to a growing roll, the invention has recognized that the tension of the web to be wound, i.e., the tension of the part of the web before the web reaches the roll, is to be reduced.
WELP, Ewald G. discloses in the paper Papier-und Kunststoff-Verarbeitung, September 1981, page 54 to 59, two drum winders with constant back tension in dependence on the roll diameter. A change of overspeed and different torque of the two drums is discussed. In what manner the torque is to follow the diameter of the roll is not mentioned.
FORSBERG, G. proposes in Paper Trade Journal, Apr. 28, 1969, page 36 to 40, to put almost all the torque into the front drum at the start and then gradually to transfer the torque from the from drum to the back drum.
KLEIN, Hugo Rollenschneid-und Wickelmaschinen. In: Papier und Kunstoff-Verarbeiter, 11-77, 5.28-40; Firmenschrift der Jagenberg-Werke G. Dusseldorf. Technische Informationen, III/314, eing. I: DPA 30.8 1965, S. 1-4, discloses a two drum winder, the front drum current of which decreases linearly, while the back drum current increases. Neither a dependence of the back tension on the diameter of the roll nor a dependence of the front drum torque during beginning or end of the winding process is revealed. Further, this document reveals a decrease of the pressure exerted by a rider roll in dependence on the diameter of the roll.